Many type of molded semiconductor packages have a so-called LTI (lead tip inspection) feature at the edge of the molded package to allow for optical inspection of the joint or bond between the metal pads of the molded package and a substrate to which the molded package is attached such as a circuit board. The LTI feature is the portion of a metal pad at the periphery of a molded package which extends to the edge of the molded package and is uncovered by the mold compound, thus allowing for optical inspection from the side.
Individual molded packages are typically formed from a molded substrate which includes a number of semiconductor dies and metal pads electrically connected to the dies. The semiconductor dies and the metal pads are embedded in a mold compound. The metal pads are uncovered at the bottom surface of the mold compound. Metal pads of adjacent packages are connected. These connections are severed by a mechanical sawing process. The exposed part of each cut metal pad forms an LTI feature at the side of the individual molded package, which is uncovered by mold compound as a result of the package singulation process.
However, a two-step sawing process is typically employed to realize LTI features. Also, metal burrs are often present on the LTI features as a result of the two-step sawing process. The metal material of the pads can smear during sawing. In both cases, the likelihood of successful optical detection is reduced due to the degraded LTI feature. Alternatively, LTI features can be realized by a selective etching process with electroless plating. However, selective etching is limited to the leadframe supplier and requires a suitable anisotropic copper etchant.
As such, a simpler and more cost effective technique is needed for manufacturing molded semiconductor packages having an optical inspection feature.